A vapour scare forced the evacuation of small children from Leisurelink Aquatic Centre at Waurn Ponds on Wednesday night.
Paramedics rushed 16 people, including children, to hospital after they reported breathing difficulties.
City Hall investigations on Thursday revealed that the swimming centre had experienced a power outage for 30 minutes just before the incident.
“When power was restored, the plant room resumed injecting disinfectant agent (liquid chlorine) into the pool water,” the City’s spokesperson Geoff Russell said.
“This caused a natural chloramines reaction, which resulted in an elevated odour, especially in the children’s pool area.
“We believe this odour led to some breathing irritation for some of the children in the pool at the time.”
The pool’s staff evacuated about 100 people and called emergency services.
Paramedics took 12 people to Geelong hospital and four to Epworth Geelong in Waurn Ponds.
Barwon Health urged locals to only go the emergency department for serious or life-threatening conditions in response to the incident.
“Due to an incident at Leisurelink Waurn Ponds, the University Hospital Geelong Emergency Department is at increased demand,” the authority posted.
Barwon Health later posted online that the patients appeared to have avoided serious injury.
“These individuals are currently under observation in our short stay unit and are showing no signs of illness,” it posted.
The pool reopened on Thursday following Worksafe approval, Mr Russell said.
“We have determined that at no time was there a leak of any form of gas.
“The City of Greater Geelong regrets and apologises for any discomfort or distress caused to patrons of its, involved in last night’s incident.
“Our computer records also indicate that at no time did the disinfectant dosing levels into the pool exceed normal limits, set by health authorities.”
City Hall chief executive officer Kelvin Spiller praised the pool’s staff for their reaction.
“I’m very proud to say that our pool staff took immediate action and evacuated everyone from the centre in a calm and professional manner,” he said.
“Several of our staff also complained of sore throats, and were examined by paramedics. Some parents chose to take their children to hospital for further assessment and advice.”
Mr Spiller apologised for the worry the incident caused for parents or children.
“We would all prefer that such incidents never occurred,” he said.
Belmont, Geelong, Grovedale and Corio CFA brigades attended the incident and hazmat crews tested chlorine and pH levels.